Schiff Base Formation Research Articles

Selective Schiff Base Formation of Group 9 Organometallic Complexes with Functionalized Spirobifluorene Ligands.

Organic amines are important compounds present in a wide variety of products, which makes the development of new systems for their detection an interesting field of study. New organometallic complexes of group 9 [MCp*X(2'-R-2-py-SBF)] (M = Ir, Rh; R = H, X = Cl (6), R = H, X = OAc (7), R = CHO, X = Cl (8)), and [IrCp*Cl(2', 7-diCHO-2-py-SBF)] (9) (Cp* pentamethylcyclopentadienyl, SBF = 9,9'-spirobifluorene) bearing bidentate C-N ligands based on 9,9'-spirobifluorene were obtained and characterized by NMR spectroscopy, mass spectrometry, IR spectroscopy, and X-ray diffraction analysis when possible. The formation of a Schiff base to give complexes with the formula [MCp*Cl(2'-CH=NR-2-py-SBF)] (M = Ir, Rh; R = alkyl or aryl (10-12)), through condensation of an amine, and the aldehyde group present in these new complexes was studied leading to a selective reactivity depending on the nature of the amine and the metal center. While the iridium complexes only react with aromatic amines, the rhodium derivative requires heat for those but can react at room temperature with aliphatic amines.

Preparation, physicochemical and biological evaluation of chitosan Pleurotus ostreatus polysaccharides active films for food packaging

The aim of this study was to create CS-POP composite films by blending Pleurotus ostreatus stalk polysaccharides (POP) and chitosan (CS). The effects of adding different concentrations (0 %, 0.25 %, 0.5 %, 0.75 %, and 1 %) of POP on the mechanical, barrier, and optical properties of the CS films were investigated. When the POP content is at 0.5 %, the tensile strength of the composite film reaches its maximum value at 13.691 MPa, showing a significant improvement compared to the tensile strength of the pure CS film. The structure of the CS and CS-POP composite films was characterized by FT-IR spectroscopy, XRD, TGA and SEM. The results indicate that due to the interaction between the two types of CS and POP, the formation of Schiff base, and the intermolecular hydrogen bonds between CS and POP, the addition of POP to CS films can result in a smoother and more stable crystalline structure in the composite film. The CS-POP composite films exhibited enhanced antioxidant and antibacterial activity compared to the CS films alone, with the highest DPPH scavenging activity of 72.43 %. The composite films also showed significant inhibitory effects on the growth of E. coli.

Physicochemical and in vivo evaluation of crosslinked carboxymethyl chitosan-gelatin scaffolds for wound healing application

This study intends to fabricate new antimicrobial scaffolds based on crosslinked Carboxymethyl chitosan (CMCh)/gelatin (Gel) biopolymers. While the physical and morphological characteristics of the crosslinked scaffolds were investigated using the swelling index, hydrolytic degradation study, moisture permeation study, surface roughness profiling, and tensile strength study, their chemical crosslinking was proved using FTIR spectroscopy and DSC analysis. Moreover, antibacterial study, MTT assay, and in vitro scratch assay were also conducted to get more information about the inherent antibacterial, cytocompatible and in vitro wound healing potential of the developed scaffolds. Further, the effectiveness of developed scaffolds was also assessed using an in-vivo incision wound study. FTIR and DSC studies confirmed the crosslinking of polymers at low concentrations of glut by the formation of Schiff base. Further, swelling index, hydrolytic degradation, tensile strength, and roughness of the scaffolds varied with both polymer ratio and concentration of the crosslinking agent. Additionally, scaffolds showed inherent antibacterial properties against gram-positive and gram-negative bacteria strains and exhibited excellent cell viability at lower concentrations of crosslinker. In-vitro wound healing scratch assay revealed proliferation and migration of cells when treated with scaffolds compared to control and standard treated formulation. Further, the TS of the healed wound indicated the quality of healing of the incision wound which was found to be higher for the group treated with an optimized scaffold in comparison to other groups. Thus, our findings show that developed scaffolds have a high applicative potential that can be studied further for biomedical applications such as skin tissue regeneration and wound healing.

Fluorescent dendritic fibrous nanosilica/polyurethane composite membranes for selective and sensitive recognition and removal of Hg2+/Hg+ ions

Dendritic fiber nanosilica (DFNS) possesses a unique porous structure, and its potential application for adsorption and separation, particularly of heavy metals, should be explored. This study, to our knowledge, is the first time to introduce fluorescence recognition ability to DFNS and to combine it with polymer materials. Firstly, the fluorescent DFNS (FL-DFNS) was prepared by a Schiff base formation reaction between the naphthalamide fluorophore and the modified DFNS. Then, a two-step approach was employed to fabricate FL-DFNS/polyurethane (FL-DFNS/CSPU-02) nanocomposite materials. FL-DFNS functions as a “turn off” sensor for Hg2+/Hg+ ions, exhibiting fluorescence quenching of up to 81.1 %/75.9 %. It also has an excellent adsorption capacity to mercury. Specifically, FL-DFNS/CSPU-02 membrane enabled portable detection of Hg2+/Hg+ ions. Importantly, it exhibited superior performance in the adsorption and separation of Hg2+/Hg+ ions, achieving a removal efficiency of 97.7 % and 98.0 %, with an absorption capacity of 382.4/373.5 µg/cm2. And it can be recycled for at least nine times. Overall, this study confirms the practical application value of FL-DFNS and FL-DFNS/CSPU-02 membrane in the recognition and removal of Hg2+/Hg+ ions, it will achieve the real application in environmental science and engineering.

Dual preservative strategy for facilitating bamboo durability using cinnamaldehyde and diethylenetriamine and its reaction characteristics on bamboo cell wall

Cinnamaldehyde exhibits excellent anti-mold properties that can preserve bamboo. However, establishing a stable bonding linkage (CN) requires cinnamaldehyde modification, which can be used to manipulate cell wall characteristics and improve bamboo durability. In this study, cinnamaldehyde's chemical fixation into bamboo through the Mannich reaction was successfully achieved, resulting in enhanced anti-mold capacity and dimensional stability. The modified bamboo exhibited remarkable anti-mold properties, with a 40.0% increase in resistance to swelling caused by moisture fluctuations. Nanoindentation analysis also revealed that the internal bamboo cell wall's mechanical properties improved following modification, including a significant improvement in surface hydrophobicity from 13.9° to 67.3°. Concerning the impact of the modification on bamboo cells, the sclerenchyma cell of bamboo was determined to be the focus. We used guaiacol as a lignin model compound to elucidate the potential mechanism of cinnamaldehyde modification, specifically Schiff base formation, using nuclear magnetic resonance spectra. This study shows a viable dual preservative strategy to extend bamboo lifespan.

Fe3O4-chitosan immobilized Cu(II) Schiff base catalyst for the microwave-assisted amination of aryl halides in water

This work represents the synthesis, characterization, and application of a magnetically separable (Fe3O4@CS@AF@Cu) catalyst for the C-N coupling reaction towards arylation of amines. The catalyst is synthesized by modifying the surface of Fe3O4-chitosan with acetyl-2-furan (AF) via the formation of Schiff base and then, generating a Cu(II) complex on the functionalized surface. State-of-art characterization techniques such as Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectrometry (EDX), transmission electron microscopy (TEM), X-ray diffractometer (XRD), x-ray photoelectron spectroscopy (XPS) and inductively coupled plasma-optical emission (ICP-OES) spectrometry have been used to verify the structure of the catalyst. Under microwave irradiation, the Ullmann C-N coupling reactions using various aryl halides and amines demonstrate exceptional catalytic performance with a minimal catalyst loading of 0.63 mol% of Cu. Furthermore, the catalyst has been recycled 5 times with 96% efficiency for the amination of 1-bromo-4-nitrobenzene with piperidine under the investigated conditions. Overall, this study provides a practical approach to the synthesis of an effective heterogeneous catalyst for the C-N coupling reaction, which can be used in pharmaceuticals, bulk, and fine chemical industries.

Metal Free Simple and Efficient Synthesis of Tetrahydropyrrolo[1,2-a]- Pyrazine Based on a Cascade Strategy

Abstract: A simple and efficient synthesis of pyrrolo[1,2-a]pyrazine using Schiff base formation, intramolecular cyclization (or N-alkylation), and Pictet–Spengler type reaction (hetero-aromatisation) has been developed. In this chemistry, metal-free, cost and time-effective processes have been highlighted to afford the complex nitrogenous scaffold using simple starting materials.

Discovery of a cystathionine γ-lyase (CSE) selective inhibitor targeting active-site pyridoxal 5′-phosphate (PLP) via Schiff base formation

D,L-Propargylglycine (PAG) has been widely used as a selective inhibitor to investigate the biological functions of cystathionine γ-lyase (CSE), which catalyzes the formation of reactive sulfur species (RSS). However, PAG also inhibits other PLP (pyridoxal-5′-phosphate)-dependent enzymes such as methionine γ-lyase (MGL) and L-alanine transaminase (ALT), so highly selective CSE inhibitors are still required. Here, we performed high-throughput screening (HTS) of a large chemical library and identified oxamic hydrazide 1 as a potent inhibitor of CSE (IC50 = 13 ± 1 μM (mean ± S.E.)) with high selectivity over other PLP-dependent enzymes and RSS-generating enzymes. Inhibitor 1 inhibited the enzymatic activity of human CSE in living cells, indicating that it is sufficiently membrane-permeable. X-Ray crystal structure analysis of the complex of rat CSE (rCSE) with 1 revealed that 1 forms a Schiff base linkage with the cofactor PLP in the active site of rCSE. PLP in the active site may be a promising target for development of selective inhibitors of PLP-dependent enzymes, including RSS-generating enzymes such as cystathionine β-synthase (CBS) and cysteinyl-tRNA synthetase 2 (CARS2), which have unique substrate binding pocket structures.

Behaviors and interactions during hydrothermal carbonization of protein, cellulose and lignin

Proteins participation will inevitably reconstruct the conversion route of lignocellulosic components and the formation of N-containing hydrochar during hydrothermal carbonization process. Herein, the behaviors and interaction mechanisms of protein, and typical biomass model chemicals (i.e. cellulose and lignin) were in-depth investigated. Results showed that the interaction of the binary mixture led to a reduction of hydrochar yield, but increased nitrogen concentration in hydrochar. Nitrogenous heterocyclic structure of hydrochar increased due to the interaction of protein with cellulose/lignin via forming Schiff bases and melanoids, wherein the content graphitic and pyridine nitrogen in protein-lignin hydrochar substantially increased from 5.4 % and 2.3 % to 9.7 % and 25.8 %, respectively. The increased ID/IG value from 0.81 to 0.91 in cellulose-protein hydrochar indicated the concentration of fused aromatic rings (≥6) based on Raman analysis. Carbon defects and disordered structure in hydrochar dramatically grew with the occurrence of the Maillard reaction and aldol-condensation of the intermediates. The nitrogenous substance in the aqueous phase increased by 30 %, resulted from protein decomposition accelerated by the hydrolysis of cellulose. This study provides a full understanding towards the transformation process of hydrochar from protein-containing biomass.

Design and tuning of monodisperse microporous ternary hydrogels of GO-MgFe2O4-Gelatin for removing divalent metal ions: Doping optimization and insights into adsorption mechanism

The current work proposes the synthesis of a scalable gelatin hydrogel doped with graphene oxide (GO) and magnesium ferrite (MF) through direct compounding and drip emulsification procedures. The composite hydrogel is studied in static conditions to investigate its applicability in large-scale continuous flow systems. The cross-section of the hydrogel showed how nanofillers were uniformly dispersed inside the polymer matrix. The process of crosslinking improved the pH resistance of the hydrogel through a Schiff base formation. The composite's point of zero charge (pHzpc) is estimated as 6.7. The ternary composite hydrogel exhibited 97 % and 91 % uptake efficiency for Ni(II) and Cd(II) respectively at static conditions. The effective removal of Ni (II) and Cd (II) ions is due to the synergistic involvement of GO, MF, and Gelatin (Gel). XPS findings reveal that Ni (II) and Cd (II) were present as oxides and hydroxides on the GMG5 surfaces. A combination of physical and chemical interactions such as surface complexation, ion exchange, electrostatic interactions, and dipole-dipole interactions catered to the improved uptake of metal ions. The hydrogel rendered stable adsorption-desorption characteristics up to three regeneration cycles with 0.1 M CH3COOH as a desorbing agent. The initial desorption efficiency was 75% for Ni (II) and 56% for Cd (II).

Reactivity and mechanism of the reactions of 4-methylbenzoquinone with amino acid residues in β-lactoglobulin: A kinetic and product investigation

Quinones, produced by the oxidation of phenolic compounds, covalently bind to nucleophilic groups on amino acids or proteins. In this study, the reactions of 4-methylbenzoquinone (4MBQ) with β-lactoglobulin (β-LG) and amino acids at neutral pH were investigated. LC-MS analysis revealed that Cys121 was likely the most modified residue in β-LG. Identification of reaction products by LC-MS/MS showed that Michael addition occurred in all reactions with amino acids tested. The formation of Schiff base and a di-adduct was found in His and Trp samples. Apparent second-order rate constants (k2) were determined at 25 °C and pH 7.0 by stopped-flow spectrophotometry. The rate of reactions decreased in the order: β-LG > His > Trp > Arg > Nα-acetyl His > Nα-acetyl Arg > Nα-acetyl Trp. The rate constants correlated with the pKa values of the amino acids, showing that the amount of unprotonated amine is the major factor determining the reactivity.

Synthesis, crystal structures and anticancer studies of Ni (Ⅱ), Co (Ⅲ) and Zn (Ⅱ) complexes based on 5-bromosalicylaldehyde- 2-(2-aminophenyl)benzimidazole Schiff base

Three metal complexes [Ni2 (HL)2 (C2H5OH)2 Cl2]·2C2H5OH (complex 1), [Co (HL) (L)] (complex 2) and [Zn2 (HL)2 (CH3COO)2] (complex 3) derived from 5-bromosalicylaldehyde-2-(2-aminophenyl)benzimidazole Schiff base ligand (H2L) were synthesized and characterized by infrared (IR) spectroscopy, thermogravimetric (TG) analysis and powder X-ray diffraction (XRD). Single crystal X-ray diffraction analysis confirmed that complex 1 crystallized in binuclear octahedral structure with space group P21/C and complex 2 displayed in mononuclear octahedral structure with space group P 121/c 1. While complex 3 produced binuclear pyramid structure with space group P 121/c 1. Herein, cobalt (Ⅱ) salt was oxidized to form Schiff base cobalt (Ⅲ) complex by coordinating three deprotonated groups. The MTT method was employed to determine the three complexes in vitro cytotoxicity effects against human lung cancer cells (A-549), liver cancer cells (SMMC-7721), breast cancer cells (MDA-MB-231) and nasopharyngeal carcinoma cells (CNE-2Z). The results showed that Co (Ⅲ) complex has significant anticancer activity against human breast cancer MDA-MB-231 cells compared with cisplatin. The further study of its anticancer mechanisms exhibited that Co (Ⅲ) complex could inhibit MDA-MB-231 cells proliferation through both apoptosis and DNA replication inhibition.

Catalytic Hydrogenation of Furfural over UiO‐66‐NH2‐derived Ru‐based Catalysts: Precursor Coordination Structure for Enhanced Catalysis

AbstractThe −NH2 in UiO‐66‐NH2 was functionally modified with 2‐pyridinecarboxaldehyde to form Schiff base UiO‐66‐Pyr, and hollow nitrogen‐doped porous carbon‐ZrO2 supported Ru (Ru/NC‐ZrO2) was prepared from Ru3+‐coordinated UiO‐66‐Pyr‐Ru. Then the furfural hydrogenation performance of the product was investigated. Compared with single‐tooth‐coordinated UiO‐66‐NH2, the 2‐tooth‐coordinated UiO‐66‐Pyr can improve the stability of Ru3+ coordination and thereby increase the Ru loading and dispersity in the Ru/NC‐ZrO2, showing high furfural hydrogenation activity. The direct hydrogenation with hydrogen as the hydrogen source and the transfer hydrogenation with isopropanol as the hydrogen donor was determined by the furfural hydrogenation of Ru/NC‐ZrO2 under hydrogen or nitrogen.

Synthesis, in vitro α-glucosidase, urease activities and molecular docking study of benzoxazole bearing Schiff base derivatives

We have synthesis seventeen benzoxazole bearing Schiff base derivatives (1-17), characterized through different spectroscopic techniques i.e., 1H-NMR, 13C-NMR and HREI-MS and were screened against alpha-glucosidase and urease enzymes. All derivatives showed good inhibitory potential with IC50 value ranging from 3.20 ± 0.10 to 38.10 ± 0.20 µM (α-glucosidase) and 2.70 ± 0.40 to 21.20 ± 0.10 µM (urease) in the presence of reference drugs acarbose and thiourea having an IC50 values 38.45 ± 0.80 µM and 21.25 ± 0.15 µM respectively. Methoxy substituted derivative 1 was found most potent against alpha-glucosidase enzyme and derivative 3 was found most potent against urease enzyme. Structure activity relation has been carried out which mainly depend upon the type, number, position and electron donating/withdrawing effects of substituent(s) on phenyl ring. The study was further validated by molecular docking to find the binding interaction of most potent compounds with the enzyme active sites. All Compounds were verified for cytotoxicity against 3T3 mouse fibroblast cell line and detected non-toxic. The compounds were synthesized by simple modes of synthesis like carboxylate, hydrazide and finally Schiff base formation.

Synthesizing and post-synthetically modifying metal-organic frameworks (Co(BDC)-NH2) for carbonylative sonogashira coupling reaction

In this study, a new functionalized metal-organic framework (MOF) [Co(BDCNH2)@Schiff-Base-Pd(II)] catalyst was synthesized using the post-synthetic modification of the Co(BDCNH2). The target MOF complex was formed by adding palladium chloride while binding di(pyridin-2-yl)methanone via a basic Schiff base formation reaction. The synthesized functionalized MOF was utilized as a highly efficient multifunctional catalyst in the Sonogashira carbonylative coupling reaction. Various analytical techniques elucidated the catalyst, including N2 isotherms, XPS, EDX FT-IR, XRD, SEM, ICP-OES, and TG-DTA. Notably, the synthesized Nano catalyst is reusable up to seven times with no considerable catalytic efficiency loss, high product yields, ease of extraction, short reaction times, and a wide range of substrates make this procedure environmentally friendly.

Insight into the formation mechanism of soy protein isolate films improved by dialdehyde starch with different degrees of aldehyde substitution

Protein and polysaccharide materials are gaining attention as potential solutions for environmental pollution and reducing dependence on fossil resources. In this research, films were formed by crosslinking soy protein isolate (SPI) with dialdehyde starch (DAS) of varying aldehyde group contents. The aim was to evaluate the influence of the content/degree of aldehyde groups of DAS upon the basic properties of SPI-based films and propose a formation mechanism. Results showed that adding DAS improved the hydrophobicity, UV-blocking properties, and thermal stability of the films. The tensile strength of the film was increased from 2.95 to 7.94 MPa. The reaction between DAS and SPI formed Schiff base reactions and covalent imine bonds (CN), along with a network of hydrogen bonds. In addition, atomic force microscopy indicated that the addition of DAS resulted in an increase in the surface roughness of the films to 19.2 nm, favoring hydrophobicity and UV-barrier properties. These results provide a solid theoretical basis for further research on SPI-DAS composites.

Zein/chitosan composite nanospheres for controlled release of fragrances

The controlled release of fragrances is critical for cosmetics industry, but most traditional fragrance carriers have some limitations. In this study, ethanol soluble protein zein was selected as the matrix to encapsulate ethanol soluble cinnamaldehyde (CA) with the addition of another natural polymer chitosan (CS), forming composite nanospheres. The zein/CS composite nanospheres showed three different structures depending on the zein/CS mass ratio. The hydrophobic interaction between CA and zein, and the formation of Schiff base between CA and CS significantly reduced its volatilization rate to the air. In addition, it was found that the loading capacity, encapsulation efficiency, controlled release property, and antibacterial activity of the CA-loaded zein/CS composite nanospheres were closely related to their structure. The nanospheres with core (zein)/shell (CS) or homogenous structure displayed long CA release time (more than 1 day) and sustained antibacterial activity against Staphylococcus aureus. Therefore, the CA-loaded zein/CS composite nanospheres are promising carriers for developing antibacterial perfumes and coatings.

Local energy decomposition (through methanol), biological activity prediction, solvents interaction (DFT) and molecular docking simulation studies of Schiff base: synthesis, characterization and fluorescence properties

The compound PYANV was characterized by infrared, UV–Visible, fluorescence, and 1H-13CNMR spectral analysis. The DFT calculation was done in the structure of the molecules. The electronic spectra were done in experimental and calculated (DFT). The 1H and 13CNMR spectra peak present in 9.42 (s,1H) ppm and 165.09 ppm respectively, these peak confirm the Schiff base formation. In electronic spectrum we observed two different wavelength which is 329 nm and 405 nm. The fluorescence spectrum also shows two different wavelength such as 499 nm and 666 nm, with exciation of 320 nm. The FT-IR section we observed -CN stretching vibration at 1689 cm−1, this vibration mention the formation of azomethine group. The HOMO-LUMO and MEP studies were done with the gas phase and four different solvents. Topological analysis (ELF, LOL, ALIE) provides about interactions between and within molecules. The RDG (non-covalent) interactions were calculated and analyzed inter and intramolecular hydrogen bonding. NBO calculation represented inter and intra-molecular interactions. A docking study of the compound was done, and docking simulation study results show that PYANV has good interaction against 7RJC protein, and highest binding energy is −5.72 kcal/mol and −6.28 kcal/mol for synthezied compound and standard.

Amino-Acid-Derived Oxazolidin-5-Ones as Chemical Markers for Schiff Base Formation in Glycation Reactions

Imine or Schiff base formation is considered as a key event in the catalytic mechanisms of many enzymes and in certain biological transformations, including glycation. In this process, less stable amino-acid-derived Schiff bases rearrange into more stable ketoamines or Amadori products. Schiff bases are also stipulated to be stabilized through complexation with metal ions, or through intramolecular cyclization to form more stable and reversible cyclic isomers, such as oxazolidin-5-ones. These intermediates can be easily detected relative to Schiff bases due to their higher stability. In this study, high-resolution mass spectrometry and isotope labeling techniques were used to identify labile imines as their oxazolidin-5-one derivatives in heated reaction systems of glucose/alanine/FeCl2, including their 13C-labeled counterparts. The reaction mixtures were heated for 2h at 110 °C and were analyzed by high resolution qTOF/MS for the presence of masses corresponding to Schiff bases of α-alanine with short chain aldehydes that can be generated from glucose degradation and also for the incorporation of 13C-labeled atoms from 13C-3 alanine and 13C-U glucose. Analysis of the data has indicated that Schiff bases can indeed be detected in the form of oxazolidin-3-ones, when methanol is used as the solvent. Furthermore, it was discovered that metal-ion-stabilized Schiff bases, in addition to forming oxazolidin-3-ones, can also undergo aldol addition with short chain sugars and initiate oligomerization reactions, leading to the formation of dimeric or trimeric oxazolidin-3-one oligomers, as demonstrated by their characteristic MS/MS fragmentations.

Multi-Detection Size Exclusion Chromatography as an Advanced Tool for Monitoring Enzyme-Antibody Conjugation Reaction and Quality Control of a Final Product.

The multi-detection size exclusion chromatography (SEC) has been recognized as an advanced analytical technique for the characterization of macromolecules and process control, as well as the manufacturing and formulation of biotechnology products. It reveals reproducible molecular characterization data, such as molecular weight and its distribution, and the size, shape, and composition of the sample peaks. The aim of this work was to investigate the potential and suitability of the multi-detection SEC as a tool for surveillance over the molecular processes during the conjugation reaction between the antibody (IgG) and horseradish peroxidase (HRP), and demonstrate the plausibility of its application in the quality control of the final product, the IgG-HRP conjugate. Guinea pig anti-Vero IgG-HRP conjugate was prepared using a modified periodate oxidation method, based on periodate oxidation of the carbohydrate side chains of HRP, followed by the formation of Schiff bases between the activated HRP and amino groups of the IgG. The quantitative molecular characterization data of the starting samples, intermediates, and final product were obtained by multi-detection SEC. Titration of the prepared conjugate was performed by the ELISA and its optimal working dilution was determined. This methodology proved to be a promising and powerful technology for the IgG-HRP conjugate process control and development, as well as for the quality control of the final product, as verified by the analysis of several commercially available reagents.